JPH02142809A - Methacrylate copolymer - Google Patents

Abstract

PURPOSE:To improve the transparency, heat resistance, low birefringence and low water absorbency by reacting methyl methacrylate with a specific N- substituted maleimide compound, an aromatic vinyl compound and benzyl methacrylate. CONSTITUTION:30-90wt.% methyl methacrylate (A) is copolymerized with 5-35wt.% N-substituted maleimide compound (B) of formula I [wherein R is H, 1-4C alkyl, cyclohexyl, benzyl or (un)substituted aryl], 0-15wt.% aromatic vinyl compound (C) of formula II (wherein X is H or methyl; Y is H, halogen or 1-4C alkyl; and h is 1-3) and 0-35wt.% benzyl methacrylate (D) of formula III (wherein Z is Y; and i is 1-3) in the presence of a polymerization initiator (e.g., 2,2'-azobisubutyronitrile), thereby producing a methacrylate copolymer which satisfies 5<=c+d when c/b+d<=0.3 wherein the wt.% of units of the components (A) to (D) are a to d respectively.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to methacrylic copolymerization, and more particularly to a copolymer for optical materials having excellent transparency, heat resistance, low birefringence, and low water absorption. It is related to.

[Conventional technology]

Plastics are often used as materials for optical materials such as lenses and optical disk substrates. For example, acrylic resin or polycarbonate resin is used for optical disk substrates, but the required performance of optical disk substrates is, of course, that they must be transparent so that laser beams can pass through them.
Optical homogeneity is strongly required to reduce reading errors. However, although using plastic as an optical disk substrate makes it possible to mold a large number of replicated substrates at low cost, birefringence occurs during substrate molding, and optical inhomogeneity due to this large birefringence occurs. This is a fatal flaw in optical disk infrastructure. On the other hand, the types of disks have progressed to read-only, write-once, and erasable types, and new recording materials have been developed, and the substrate becomes considerably hot during the deposition of recording materials and during recording, playback, and erasing using laser beams. is predicted. Therefore, optical discs with poor heat resistance may warp the base or cause defects in the guide grooves, leading to reading errors, and a disc base with high heat resistance is desired. Furthermore, there is a risk of deterioration of the recording material due to water absorption and reading errors due to warping.
There is a need for a substrate that also has low water absorption. Polycarbonate, which is currently used as a disk substrate, has good heat resistance and water absorption, but has large birefringence, while acrylic resin has low birefringence, but has low heat resistance and large water absorption. .

- On the other hand, the same is true for lens materials; materials that have not only transparency but also optical homogeneity and low water absorption are desired, and improvements in heat resistance are also desired in order to expand the range of use.

Against this background, various attempts have been made to improve the heat resistance of acrylic resins while maintaining their birefringence.For example, methyl methacrylate and
-Copolymers consisting of methylphenylmaleimide (JP-A-1-217216), copolymers consisting of methyl methacrylate and maleimide monomers, or methyl methacrylate, maleimide monomers and other vinyl Copolymers (JP-A-61-95011, JP-A-62-87901) made of monomers have been proposed. In addition, as a method for improving water absorption, for example, a method of copolymerizing methyl methacrylate and styrene (Japanese Unexamined Patent Publication No. 57-3
3446), a method for copolymerizing methyl methacrylate and cyclohexyl methacrylate (Japanese Unexamined Patent Publication No. 57-186)
241, JP-A-58-127754) or a method of copolymerizing methyl methacrylate and benzyl methacrylate (JP-A-58-11515).

[Problem to be solved by the invention]

However, in the proposed method, heat resistance, water absorption,
Although some effects can be observed when one or all three types of birefringence are considered, it is difficult to satisfy all three at the same time, and it is difficult to satisfy all three types at the same time. I haven't gotten anything.

Therefore, an object of the present invention is to provide a copolymer for optical materials that has excellent transparency and is also excellent in heat resistance, low water absorption, and low birefringence.

[Means to solve the problem]

In order to obtain a copolymer with the above-mentioned properties, the present inventors have conducted extensive studies on acrylic copolymers containing N-substituted maleimide as one component, and have surprisingly found that methacrylic acid has a specific blending composition. This was achieved for the first time with a copolymer obtained by copolymerizing a mixture of methyl, an N-substituted maleimide compound, an aromatic vinyl compound, and/or a hensyl methacrylate compound, and it is suitable for use as a material for high-quality optical materials. This finding led to the completion of the present invention.

That is, the present invention provides (A) methyl methacrylate unit 3
0 to 90% by weight, the general formula (B) represents a hydrogen atom, a halogen atom, or an alkyl group having 1 to 4 carbon atoms, and h is 1
0 to 15% by weight of aromatic vinyl compound units represented by (representing an integer from 1 to 3) and (D) general formula (wherein R is a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, a cyclohexyl group, a hensyl group) , a substituted or unsubstituted aryl group) 5 to 35% by weight of N-substituted maleimide compound units represented by the general formula (C) (wherein X represents a hydrogen atom or a methyl group, Y (in the formula, Z
represents a hydrogen atom, a halogen atom, or an alkyl group having 1 to 4 carbon atoms, and i represents an integer of 1 to 3. A methacrylic copolymer that satisfies c/(b0d)≦0.3 and 5≦c+d, where c and d are the weight percentages of maleimide compound units, aromatic vinyl compound units, and hensyl methacrylate compound units, respectively. It provides integration.

[For production]

(A) used in the methacrylic copolymer of the present invention
) The methyl methacrylate unit is the main monomer unit of the copolymer, and plays a role in improving transparency and mechanical strength, and its content varies with respect to the copolymer. It ranges from 30 to 90% by weight, preferably from 35 to 85% by weight. If the content is less than 30% by weight, transparency and mechanical strength will decrease, which is undesirable. On the other hand, if it exceeds 90% by weight, the effect of improving heat resistance and low water absorption will be small, which is undesirable.

(B) which is the other main unit used in the present invention
The N-substituted maleimide compound unit has a structure represented by the above general formula (1), and plays a role in improving the heat resistance and thermal stability of the copolymer. Its content is 5 to 35% by weight, preferably 10 to 30% by weight based on the copolymer.
is within the range of

If this content is less than 5% by weight, the effect of improving heat resistance will be small, which is undesirable, and if it exceeds 35% by weight, transparency and mechanical strength will decrease, which is not preferred. Examples of this N-substituted maleimide compound unit include N-cyclohexylmaleimide, Ntertbutylmaleimide-1
N-hensylmaleimide, N-phenylmaleimide, N
-(2-chlorophenyl)maleimide, N-(2-methylphenyl)maleimide, N-(2-ethylphenyl)
Examples include monomer units such as N-cyclohexylmaleimide, N-(2,6-dimethylphenyl)maleimide, N-(2,6-dinitylphenyl)maleimide, and N-cyclohexylmaleimide, N-cyclohexylmaleimide, It is a monomer unit such as (2-chlorophenyl)maleimide.

The (C) aromatic vinyl compound unit of the present invention has the general formula (
It has a structure represented by II) and plays a role in improving the water absorption of the copolymer, and its content is 0-15% by weight, preferably 2-12% by weight based on the copolymer.
Weight%. If the amount exceeds 5% by weight, the effect of improving low birefringence is small and undesirable. Examples of the aromatic vinyl compound unit include styrene, vinyltoluene, α-methylstyrene, 4-chlorostyrene, 4-
Examples include monomer units such as halogenated styrene such as bromostyrene, among which monomer units such as styrene, 2-methylstyrene, 4-methylstyrene, and α-methylstyrene are preferred.

Furthermore, the benzyl methacrylate compound unit (D) of the present invention has a structure represented by the general formula (1) above, and plays a role in improving the water absorption of the copolymer, and its content is controlled by the copolymer. The amount is 0 to 35% by weight, preferably 5 to 30% by weight, based on the polymer. If this amount exceeds 35% by weight, heat resistance and mechanical strength will decrease, which is not preferable. The hensyl methacrylate compound unit ζ is, for example, hensyl methacrylate, 4-methylbenzyl methacrylate, 4-tert-butylhensyl methacrylate, 4-chlorobenzyl methacrylate, 2,4 methacrylate.
6-) Monomer units such as ribromohensyl may be mentioned, and among these, hensyl methacrylate unit is preferred.

The copolymer of the present invention comprises (A) 30 to 90% by weight of methyl methacrylate units, (B) 5 to 35% by weight of N-J exchanged maleimide compound units represented by general formula (1), and (C)
Aromatic vinyl compound unit represented by general formula (II) 0-
15% by weight and (D) 0 to 35% by weight of hensyl methacrylate compound units represented by general formula (III),
Moreover, b is the weight percent of the N-substituted maleimide compound units represented by the general formula (1), and C1 is the weight percent of the aromatic vinyl compound units represented by the general formula (Il).
If d is the weight percent of the Hensyl methacrylate compound unit represented by I[l), c/(b+d)≦0.3, and 5
It is necessary to satisfy ≦c+d, and preferably c
/(b+d)≦0.25, force) and 10≦c10d.

If c/(b+d) exceeds 0.3, birefringence increases, which is not preferable. Moreover, if c + d is less than 5, water absorption becomes large, which is not preferable.

The method for producing the copolymer of the present invention is not particularly limited,
Bulk polymerization, suspension polymerization, solution polymerization, emulsion polymerization, etc. are possible.

As a polymerization initiator for polymerizing the copolymer of the present invention, any initiator generally used in radical polymerization can be used. For example, azo initiators such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4 dimethylvaleronitrile), lauroyl peroxide,
Peroxide-based initiators such as benzyl peroxide and tert-butylperoxy-2-conitylhexanoate can be used.

Chain transfer agents used as necessary when polymerizing the copolymer of the present invention include n-octyl mercaptan, n-
Examples include mercaptan compounds such as -dodecylmercaptan and 2-ethylhexyl thioglycolate.

Further, in the copolymer of the present invention, ultraviolet absorbers, antioxidants, lubricants, mold release agents, dyes, etc. may be added as necessary.

The copolymer of the present invention can be molded by any method such as cast molding, compression molding, injection molding, or injection compression molding, but injection molding allows for mass production because of its low birefringence. is economically advantageous.

The copolymer of the present invention obtained as described above is of high quality, having transparency equivalent to that of polystyrene or polymethyl methacrylate, and having heat resistance, low birefringence, and low water absorption. Therefore, it is an excellent material for optical materials such as optical discs and optical lenses.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples.

The abbreviations of the substance names listed in Table 1 are as follows.

MMA...Methyl methacrylate CHMI...N-cyclohexylmaleimide CPMI
...N-2-chlorophenylmaleimide St ・
...Styrene 4MS t...4-methylstyrene αMSt...α-methylstyrene BzMA...Hensyl methacrylate 4MBzMA...4-Methylhensyl methacrylate B
rBzMA: 2-bromohensyl methacrylate Further, physical properties of the resin copolymers in Examples were evaluated according to the following method.

(1) Heat distortion temperature, HDT ASTM-D648 (264PSi) (2) Total light transmittance, haze ASTM-D 1003 (1,2 thickness) (3) Equilibrium water absorption ASTM-D570 (23°C) (4 ) Tensile strength ASTM-D638 +51MF+ ASTt-D 123 B (1 condition, 230°C, 3.
(8 kg) (6) Birefringence An optical disk disk with a diameter of 130 mm and a thickness of 1.2 wsva is injection molded using a center gate mold, and the birefringence at a position 25 mm from the center of the substrate is measured using an ellipsometer (single). Pass).

Example 1 Methyl methacrylate 65% by weight, N-cyclohexylmaleimide 20% by weight, styrene 5% by weight, Hensyl methacrylate 10% by weight, lauroyl peroxide 0.2
5Phr, n-dodecylmercaptan 0.2Pb
20 kg of monomer solution consisting of r and 99.6 kg of ion exchange water
7% by weight, 50kg of an aqueous solution consisting of 0.03% by weight of a copolymer of sodium methacrylate and sodium styrene P-sulfonate, and 0.3% by weight of sodium sulfate, into a 100jl container with a jacket! The mixture was placed in a pressure-resistant polymerization tank, stirred under a nitrogen atmosphere, and hot water was passed through the jacket to initiate polymerization at 70°C.

Three hours after the start of polymerization, steam was passed through the jacket to raise the temperature of the system to 120°C, and the temperature was maintained for an additional 2 hours to complete polymerization. Uniform beads were obtained in good yield, and after being washed with water and dried, they were pelletized at 260°C using an extruder with a 60 mm diameter hent. The MFI of the pellets obtained was 1.2.
g/10mln.

Next, injection molding was performed at a cylinder temperature of 260°C and a mold temperature of 70°C to obtain a physical property test piece and an optical disk substrate. Table 1 shows the results of measuring each physical property using these.

Examples 2 to 11, Comparative Examples 1 to 6 Disc substrates were obtained in the same manner as in Example 1 except that the monomer composition was changed, and the results of measuring each of these physical properties are shown in Table 1. Ta.

〔Effect of the invention〕

As described above, the present invention provides (A) 30 to 90% by weight of methyl methacrylate units, (B) 5 to 35% by weight of N-substituted maleimide compound units represented by general formula (1), (C)
Aromatic vinyl compounds 0 to 15 represented by general formula (II)
parts by weight and (D) 0 to 35% by weight of benzyl methacrylate compound units represented by the general formula (I[l), and further comprising the N-substituted maleimide compound units, aromatic vinyl compound units and benzyl methacrylate compound units. If the weight % is c and d, then c/(b+d
)≦0.3 and 5≦c+d, it has excellent transparency, heat resistance,
It has both low water absorption and low birefringence, making it useful as a copolymer for optical materials.It also has well-balanced mechanical properties, such as optical discs and optical lenses that require heat resistance. can be provided advantageously.

Claims (2)

[Claims] (1) (A) Methyl methacrylate unit 30-90% by weight
, (B) General formula ▲ Numerical formula, chemical formula, table, etc. ▼ (In the formula, R represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, a cyclohexyl group, a benzyl group, a substituted or unsubstituted aryl group) 5 to 35% by weight of N-substituted maleimide compound units represented by (C) General formula ▲ Numerical formulas, chemical formulas, tables, etc. ▼ (In the formula, X represents a hydrogen atom or a methyl group, and Y represents a hydrogen atom or a halogen atom. or an alkyl group having 1 to 4 carbon atoms, and h represents an integer of 1 to 3) and (D) general formula ▲ mathematical formula, chemical formula, table, etc. Yes▼ (In the formula, Z is a hydrogen atom, a halogen atom, or a carbon atom number of 1~
4 represents an alkyl group, i represents an integer from 1 to 3. A methacrylic copolymer which satisfies c/(b+d)≦0.3 and 5≦c+d, where the weight percentages of benzyl compound units are b, c, and d, respectively. (2) The methacrylic copolymer according to claim 1, wherein the methacrylic copolymer is a copolymer for optical materials.